1. Field of the Invention
The present invention relates to a fire-proof coating material used for a fire-proof coating of steel frame for use in a large size architectural construction, such as a building, and for other purpose, and a fire-proof construction using the coating material.
2. Description of the Related Art
In the recent years, height of building employing a steel frame work is increasing. Associating with this, it has been an important problem to maintain rigidity of a steel frame structure even upon occurrence of fire or the like. In case of ordinary steel, heat-resistance temperature is 350xc2x0 C., and in case of heat-resisting steel, heat-resistance temperature is merely 600xc2x0 C. Therefore, the steel frame work may soften at a temperature higher than or equal to the heat resistance temperature. A fire-proof coating demonstrating quite strong heat insulation characteristics is required in order to withstand 1000xc2x0 C. of temperature at the occurrence of fire. However, asbestos conventionally used as typical fire-proof coating cannot be used for the problem of carcinogenicity due to dust inhalation. Also, for similar concern for health, rock wool cannot be suitable material for fire-proof coating.
As fire-proof material to be a replacement of asbestos or rock wool, various heat-foaming type fire-proof paints forming a heat-insulative foam layer at the occurrence of fire providing flame-proofing and heat-shielding effect, have been proposed. Some of such fire-proof paints already been put into practice. These heat-foaming type fire proof paints includes an inorganic type paint, in which a curing agent, an aggregate component are blended with taking water soluble alkaline silicate as primary component to cause foaming in response to evaporation of moisture content, and an organic type paint blended carbonizer and foaming agent to a binding resin to form carbonized layer in conjunction with foaming by foaming agent. In addition, there have been proposed a paint containing a reaction product of water soluble silicate and alkoxysilane derivative or organosilica sol, as primary component, a paint containing a mixture of water soluble alkaline silicate and ultraviolet curing resin component, and so forth.
However, in the current status, this heat-foaming type first-proof paint has been hardly practiced. Only organic type paint has been put into practice. However, even the organic type paint cannot always be used as constructional fire-proof coating under building standard laws. Furthermore, the organic type heat-foaming type fire-proof paint may maintain the temperature of the steel frame in fire-proofing performance evaluation test lower than or equal to 350xc2x0 C. only for 40 minutes as shown by correlation curve B of steel temperature-heating period of FIG. 1 and thus is quite precarious as fire-proof coating for steel frame structure. In general, the fire-proofing period of the steel frame required under applicable building standard laws may depend upon height of the building. That is, in fire-proofing performance evaluation test (JIS A1304), when the number of floors of the building as counted from the highest floor is 1 to 4, one hour fire-proofing is required. When the number of floors of the building as counted from the highest floor is 5 to 14, two hour fire-proofing is required. When the number of floors of the building as counted from the highest floor is 15 or more, three hours fire-proofing is required. Accordingly, in the prior art, even the heat-foaming type fire-proof paint satisfying one hour fire-proofing performance for the steel frame of ordinary steel has not been realized.
During study for realizing inorganic heat-foaming fire-proof paint demonstrating satisfactory heat insulation ability as fire-proof coating for the steel frame work in view of the state of art as set forth above, the inventors have found it particularly important to satisfy the following conditions [A] to [D] as foaming type coat film. Then, cause why the conventional inorganic heat-foaming fire-proofing paint has not being put into practice, is considered as lacking one or more of the following necessary conditions.
[A] To form thick foamed layer with high foaming ability as subject to heat;
[B] To generate uniform and fine bubble over the entire coat film by foaming;
[C] To have high fluidizing point (fluidizing temperature) after foaming; and
[D] To have no crack in the coat film.
In the case of the inorganic paint with water soluble alkaline silicate as primary component, it is required that the coat film may continuously maintain sufficient moisture content for ensuring satisfactory foaming ability. Furthermore, in order to uniformly generate fine bubble over the entire coat film as subject to the heat during fire disaster or other cause and to increase thickness of the entire coat film according to growth of bubble, an inorganic matrix is transformed into molten condition with sufficient viscosity upon evaporation of moisture content in the coat film. If moisture content in the coat film is too high or if viscosity of the inorganic matrix is too low, bubbles may be coupled to form void in the foamed layer or bubbles may be communicated with each other to form continuous bubble condition to lower heat insulation effect. In conjunction therewith, flowability of the foamed coat film is increased to cause dripping of the foamed substance. On the other hand, if the viscosity is too high upon foaming, the coat film can be expanded to cause rupture or can form crack. Also, in further worse case, melting of the coat film becomes insufficient to be broken into small pieces to fly off. Accordingly it is not easy to satisfy the foregoing conditions [A] and [B].
On the other hand, concerning fluidizing point after foaming as the condition [C], when the fluidizing point is low, dripping can be caused in the vertical surface, such as column surface or side surface of the beam can be caused in a short period from foaming to make the foamed layer thinner to significantly lower heat insulation ability in the thinned portion. Furthermore, concerning formation of no crack in the coat film in the condition [D], if crack is present in the coat film, heat and flame may directly reach the steel material at the position where the crack is formed, to instantly elevate the temperature of the steel material. Crack can be formed during curing of the coat film after application and may also formed due to expansion and contraction of the steel material associating to diurnal variation and seasonal variation of temperature. Therefore, it cannot be simply determine property of coat film necessary for crack prevention.
As a result of subsequent extensive experiments and study, the inventors found that when a particular fibrous mineral powder and other SiO2 providing component are blended in the heat-foaming type fire-proof paint containing water soluble alkaline silicate, suitable moisture content can be maintained in a formed coat film. This provides a surprisingly thick heat insulation layer superior in heat insulation ability without forming internal void or crack when subject to the heat. This superior heat insulation can be maintained with high fluidizing point after foaming, and formation of crack during curing of the coat film is reduced to provide superior fire-proofing performance for the steel material, such as steel frame or the like.
Accordingly, it is the first object of the present invention to provide an inorganic fire-proof coating material which can form a coat film to be transformed into a foamed layer demonstrating quite superior heat insulation ability by uniform foaming as subject to heat, such as that upon fire to prevent softening of the steel material coated by the coat film for a long enough period to be applicable as a fire-proofing coat for steel frame structure or the like. This invention also provides an inorganic fire-proof structure formed by coating the fire-proof coating material.
The second object of the present invention to provide an inorganic first-proof coating material which can be produced at low cost, facilitates formation of a smooth coat film providing superior external appearance by spray painting, forms the coat film which may not peel off by water-cannon for extinction, may not generate harmful gas or smoke, can be easily removed from a surface of a steel material after foaming, and does not cause a problem of environmental pollution, and an inorganic fire-proof structure formed by coating the fire-proof coating material.
According to one aspect of the present invention, a fire-proof coating material may be an aqueous paste comprises:
a water soluble alkaline silicate having greater than or equal to 30 Wt % solid components excluding water;
a holmite series mineral powder; and
SiO2 supplying components other than water soluble alkaline silicate and the holmite series mineral in powder form.
The holmite series mineral may be sepiolite. The holmite series mineral may be blended in a ratio of 5 to 50 Wt % with respect to water soluble alkaline silicate.
The SiO2 supplying component may be blended in a ratio to establish 3.7 to 8 of a molar ratio of SiO2/M2O in the coating material wherein M is alkali metal. In the alternative, the SiO2 supplying component may be blended in a ratio to establish 5.0 to 7.0 of a molar ratio of SiO2/M2O wherein M is alkali metal in the coating material. The SiO2 supplying component may be at least one selected among hydrolytic mica, calcium silicate, colloidal silica, natural glass, a kaolin, and perlites.
The aqueous paste may further contain titanium oxide powder. Also, the aqueous paste may further contain hydroxypropylene cellulose.
According to another aspect of the present invention, a fire-proof construction includes a steel frame formed with a fire-proof coating material set forth above, on a surface of the steel frame directly or via an undercoat layer.